Research On The Synchronous Slotted ALOHA-based Schemes For Internet Of Vehicles

The synchronous slotted ALOHA-based access schemes are more suitable for the applications of Internet of Vehicles(IoV)due to their superior performances,such as low access delay and high access capacity.Existing access schemes mainly focus on solving the problems of access collision and inter-user interference incurred by the rapid change of the network topology.To further improve the access capacity and the network throughput for IoV,this dissertation conducts and achieves the innovative research results as the following four aspects.(1)The analysis of the existing slotted ALOHA-based access schemes in IoV.Through an in-depth analysis of three types of the slotted ALOHA-based schemes in the existing IoV,it is found that the slotted ALOHA-based access mechanisms,all of which bind the request access and the data transmission,have a significant average time resource waste problem when competing for access.In addition,the slotted ALOHA-based access mechanism has an access capacity(average number of packets successfully transmitted per time slot)upper bound of only 0.37 because it is accessed as a single packet.(2)Research on the synchronous slotted ALOHA-based access scheme for request access and data transmission splitting in a single infrastructure coordination scenario.Aiming at the problem of time resource waste,this dissertation proposes a request-transmission splitting ALOHA-based(RTS-SA)access scheme that separates request access and data transmission to achieve the division of the three phases of 'request-response-transmission' within a frame,thereby obtaining an innovative access mechanism with more rational utilization of time resources.To break through the limit of the access capacity when accessed as a single packet,the RTS-SA scheme adopts a repetition code with a randomly repetitive number to construct short packets containing only vehicle identity(ID)for multiple access requests during the contention access phase.The theoretical analysis and the simulation results show that the RTS-SA scheme achieves an access capacity advantage over the traditional ALOHA-based schemes.(3)Research on suppression method of cell neighbor interference of the RTS-SA scheme in a multi-infrastructure coordination scenario.The enhanced RTS-SA(eRTS-SA)scheme is an adaptation of the RTS-SA scheme by using the information from the Global Positioning System(GPS)or BeiDou Navigation Satellite System(BDS)to aid access and time slot allocation.In the eRTS-SA scheme,each vehicle uses the location information and the vehicle ID as the request elements.Then,the infrastructure decides an optimal time slot allocation strategy based on the ascending relationship of the vehicles' location information,thus minimizing the mutual interference between the signals transmitted by the cell neighbors during the contention-free transmission phase.To reduce the overhead of requesting data,the eRTS-SA scheme also proposes a method of using relative location information between the vehicles and the infrastructure instead of accurate absolute location information,and designs the sub-optimal time slot allocation strategy based on the ascending relationship of the relative location.The simulation results show that the optimal time slot allocation strategy can be approached by the sub-optimal time slot allocation strategy using only 8-bit of quantified relative location information.To prevent broadcast interference between the adjacent infrastructures,the eRTS-SA scheme doubles the duration of the broadcast feedback phase and divides it into two equal parts,which are allocated to two adjacent infrastructures,respectively.Computer simulation results show that the eRTS-SA scheme achieves an average number of reception success of only 4.5% lower than the theoretical maximum quantity,and eRTS-SA scheme achieves about 40% and 154% increase in the average number of reception success compared to the RTS-SA and the existing slotted ALOHA-based access scheme in IoV.(4)Research on the slotted ALOHA-based access scheme in an infrastructure-free scenario.The logically centralized slotted ALOHA-based(LC-SA)scheme is based on the competitively reserved synchronous slotted ALOHA-based scheme.The LC-SA scheme solves the problem of unnecessary time slot release,thereby increasing the access success rate and the access capacity and reducing the access collision rate.The problem of unnecessary time slot release arises in the existing ALOHA-based scheme when a packet collision in the competing access a time slot,which is discarded by all competing nodes.To solve the problem of unnecessary time slot release,the selection strategy for a logically central node is first proposed in the LC-SA scheme,which guarantees the existence of only one control node in any two-hop set.Then,once the control node detects an access collision in its single-hop neighbors,it can ensure that one neighbor continues to retain the time slot.In contrast,conflicting nodes outside the communication range of the control node will give up the time slot to prevent another access collision.Simulation results show that the LC-SA scheme has higher access success rate and access capacity than the existing ALOHA-based scheme due to its lower access collision rate.Therefore,the RTS-SA,eRTS-SA,and LC-SA proposed in this dissertation have potentially significant applications considering the standardized ALOHA-based access scheme.